1) Field of the Invention
The present invention relates to a compact zoom lens suitable for a video camera and a still camera, a camera using the zoom lens as a shooting optical system, and a mobile information terminal using the zoom lens as a shooting optical system in its camera unit.
2) Description of the Related Art
Since requirements for a higher magnification, a wider angle of view, and a higher resolving power are increasing in the zoom lens for a video camera and a still camera, it is essential to reduce whole length and outer diameter of the lens, as well as the number of lenses, in order to realize small size, light weight, and low cost. As such a zoom lens, a zoom configuration has been proposed, in which a first group optical system having a positive refracting power, a second group optical system having a negative refracting power, and a third group optical system having a positive refracting power are sequentially arranged from an object side. Zooming operation is performed by increasing the interval between the first group optical system and the second group optical system, and by decreasing the interval between the second group optical system and the third group optical system, accompanying zooming from the short focal-length side to the long focal-length side.
Such type of zoom lens having a magnification exceeding 3× is disclosed, for example, in Japanese Patent Application Laid-open No. 2000-275526, Japanese Patent Application Laid-open No. H11-242157, and Japanese Patent No. 2899019.
Another zoom lens with the magnification close to 10× is disclosed, for example, in Japanese Patent Application Laid-open No. H11-109234.
However, the configurations disclosed above cannot sufficiently satisfy the requirement for a wider angle of view, since the half angle of view at the short focal-length side is as narrow as 30 degrees.
A zoom lens with the half angle of view at the short focal-length side of about 37 degrees, which corresponds to a relatively wide angle of view, is disclosed in Japanese Patent Application Laid-open No. H11-6958. However, an F value (F number) becomes F4.1 at the short focal-length side, and F5.8 at the long focal-length side, and hence the lens becomes dark. With such a dark lens, when the size of one pixel decreases, since the image capturing device such as a charge coupled device (CCD) has a high density, the performance considerably deteriorates in a high frequency domain. Therefore, it cannot satisfy the requirement for the high density sufficiently.
Japanese Patent Application Laid-open No. 2002-072088 discloses a configuration corresponding to a wide angle of view, in which the angle of view at the short focal-length side is 45 degrees or more. However, the magnification is not larger than 2×, and hence it cannot sufficiently satisfy the requirement for the high magnification.
A zoom lens miniaturized for consumer products is disclosed, for example, in Japanese Patent No. 2920549 and Japanese Patent No. 3091250, in which a first group optical system having a positive refracting power and not moving with zooming, a second group optical system having a negative refracting power and moving from an object side to an image surface side, from the wide-angle side toward the telephoto side with zooming, a third group optical system having a positive refracting power and moving from the image surface side to the object side, from the wide-angle side toward the telephoto side with zooming, and a fourth group optical system having a positive refracting power and not moving with zooming, are arranged in order from the object side to the image surface side. However, the half angle of view is only 25 degrees or less, and hence it is still not sufficient for obtaining a wide angle.
Furthermore, a zoom lens is disclosed, for example, in Japanese Patent Application Laid-open No. H6-94997, Japanese Patent Application Laid-open No. H10-62687, and Japanese Patent Application Laid-open No. H11-258507, in which the fourth group optical system in the same configuration as described above is made movable with zooming, to perform a higher degree aberration correction, realizing small size and wide angle. The zoom lens disclosed in the Japanese Patent Application Laid-open No. H6-94997 includes the whole basic configuration in this case, but does not propose a configuration requirement sufficient for achieving small size. The zoom lens disclosed in the Japanese Patent Application Laid-open No. H10-62687 aims at miniaturization by reducing the number of pieces, but sufficient aberration correction is not performed, and does not have performance that can correspond to an image capturing device with 3,000,000 to 5,000,000 pixels. The zoom lens disclosed in the Japanese Patent Application Laid-open No. H11-258507 is relatively small, and the imaging performance is better than those described above, but the half angle of view is still about 33 degrees, and hence it is still not sufficient for achieving wide angle.
There are many types of zoom lens for a digital camera. One of the conventional zoom lenses having a small size and a relatively high magnification is disclosed, for example, in Japanese Patent Application Laid-open No. 2002-133686, in which a first group optical system having a positive refracting power, i.e., a positive focal length, a second group optical system having a negative refracting power, i.e., a negative focal length, a third group optical system having a positive refracting power, a fourth group optical system having a positive refracting power, and a fifth group optical system having a positive refracting power are arranged in order from the object side. The respective lens groups are shifted at the time of zooming from the wide-angle side to the telephoto side, so that the interval between the first group optical system and the second group optical system increases; the interval between the second group optical system and the third group optical system and the interval between the third group optical system and the fourth group optical system both decrease; and the interval between the fourth group optical system and the fifth group optical system increases.
However, the magnification obtained is about 3×, which is not a sufficient value for the recent requirement for high magnification. A conventional zoom lens suitable for achieving a high magnification is disclosed, for example, in Japanese Patent Application Laid-open No. 2002-156581, in which a first group optical system having a positive refracting power, a second group optical system having a negative refracting power, a third group optical system having a positive refracting power, a fourth group optical system having a positive refracting power, and a fifth group optical system having a positive refracting power are arranged in order from the object side. A diaphragm is provided on the object side of the third group optical system; and at least the second group optical system and the fourth group optical system move with zooming from the short focal-length side to the long focal-length side. However, a magnification of about 6× can be obtained, which is still not sufficient considering the recent requirement for high magnification.